(1) Field of the Invention
The present invention relates to electro-active materials, and more specifically to devices composed of ionic polymer metal composites (IPMC) for use as bend sensors or velocity sensors.
(2) Description of the Prior Art
Electro-active materials are subject to mechanical deformation in response to external electrical stimulation or of electric current generation in response to externally induced strain. Electro-active materials are most often used as energy harvesting devices, active noise cancellation, vibration control, microphones and acoustic transducers. Electro-active polymers are also being studied for their use in artificial muscles. Recent advances and characterization of electro-active material bend sensors have exhibited a correlation between charge flow and rate of motion of the material, with relatively constant sensitivities over the frequency ranges from 0.1-20 Hz.
IPMCs are active materials that exhibit electro-mechanical coupling and consist of an ionic polymer membrane 2 with ion exchange capability (such as Nation® or Flemion®) whose planar surfaces are coated with conductors 4 such as platinum or gold, as illustrated in FIG. 1a. IPMCs have been investigated for use as actuators and motion sensors and have exhibited similar properties to piezoelectric materials. Under an applied voltage (1-5V), ion migration and electrostatic repulsion result in bending actuation. Under an applied dynamic deformation IPMC material generates a dynamic electric field with a voltage proportional to the applied force causing the deformation and with voltage polarity representative of the deflection direction. IPMC bending transducers or sensors have demonstrated relatively constant sensitivities on the order 30 μm (deflection)/mm (polymer length) over the frequency range from 0.1-20 Hz. Stacking IPMC materials as illustrated in FIG. 1b (also referred to as morphing) can increase the sensitivity of IPMC bending transducers.
One drawback of current IPMC bend sensors is that their settling time associated with a step input is on the order of 5-20 seconds for devices (on the order of 40 mm long) and increases with length. Another disadvantage of sensors and actuators fabricated with IPMCs is their inconsistent and non-repeatable step responses. Step response inconsistencies are attributable to polymer stiffness, which is a function of surface hydration. Another disadvantage of IPMC bend sensors is their limited sensitivity to deflection when compared to bend sensors of other electro-active material.
For this reason, what is needed is an IPMC bend sensor with a more consistent step response and greater sensitivity.